JP2014186768A - Optical pickup and disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical pickup capable of obtaining an excellent tracking error signal by preventing the generation of an offset component caused by stray light and to provide a disk device.SOLUTION: The optical pickup includes a plurality of light sources, an objective lens, a diffraction optical element, and a light detection part. The respective light sources emit light having mutually different wavelengths. The objective lens condenses the light on an optical disk. The diffraction optical element includes a diffraction part and a light shielding part. The diffraction part diffracts return light reflected from the first recording layer of the optical disk from and on which information is read and written. The light shielding part shields the stray light reflected from the second recording layer of the optical disk except the first recording layer. The light detection part receives the diffracted light of the diffraction optical element and generates an output signal for generating the tracking error signal on the basis of the diffracted light. Further, the light shielding part comprises a plurality of light shielding patterns shielding the light having mutually different wavelengths.

Description

  The present invention relates to an optical pickup used when reading information recorded on an optical disc and writing information on the optical disc, and a disc apparatus including the optical pickup.

  2. Description of the Related Art Conventionally, an optical pickup that reads and writes information on an optical disc such as a BD (Blu-ray Disc: registered trademark), a DVD (Digital Versatile Disc), and a CD (Compact Disc) is known. In this optical pickup, the light emitted from the light source is condensed on the recording layer of the optical disk by the objective lens.

  When reading or writing information on an optical disk by an optical pickup, it is necessary to perform tracking control so that a light spot focused on a recording layer by an objective lens always follows a track formed on the optical disk. For this reason, the optical pickup calculates a tracking error signal representing the amount of deviation between the light spot and the target track based on the signal output from the photodetector. Then, control for shifting the position of the objective lens in the tracking direction (tracking control) is performed based on the tracking error signal.

  Conventionally known methods for calculating the tracking error signal include a PP (Push-Pull) method, a DPP (Differential Push-Pull) method, and the like. In particular, since the DPP method can obtain a tracking error signal by suppressing the influence of an offset component caused by lens shift in the tracking direction of the objective lens, it is widely used in conventional optical pickups. However, in the DPP method, the light emitted from the light source is divided into three lights composed of main light and two sub-lights by a diffraction grating (grading), and is irradiated onto the optical disk. Therefore, for example, the light use efficiency is low compared to the PP method. Also, the configuration of the optical pickup becomes complicated.

  In order to improve these points, an optical pickup for obtaining a tracking error signal by a method having a simpler configuration than that of the DPP method and further improving the light utilization efficiency has been developed. For example, in the optical pickup of Patent Document 1, a part of the 0th order light and ± 1st order light reflected from the optical disk are diffracted in the main diffraction region of the diffractive optical element, and other 0th order light is diffracted in the sub diffraction region. Part is diffracted. The main light receiving unit of the light detection unit receives each 0th-order diffracted light from the main diffraction region and the sub-diffraction region, and generates a main push-pull signal. The sub light receiving unit receives ± 1st order diffracted light from the sub diffraction region and generates a sub push-pull signal. Then, the tracking error signal is generated by removing the amplified sub push-pull signal from the main push-pull signal.

International Publication No. 2011/086951

  However, the structure of the optical disc varies depending on the type (number of recording layers, type, etc.). For example, the optical disc includes a single layer type having a single recording layer and a multilayer type having a plurality of recording layers. When information reading or writing processing is performed on this multilayer optical disc, light reflected by a recording layer different from the recording layer on which the processing is performed enters the photodetector as stray light. When this stray light is received by the photodetector, an offset component due to stray light is generated in the tracking error signal, so that a good tracking error signal cannot be obtained.

  With respect to such a problem, in Patent Document 1, a diffractive optical element is provided with a rectangular light-shielding region on both outer sides of two rectangular sub-diffraction regions provided with a main diffractive region interposed therebetween. The incidence of stray light is reduced. However, in this light shielding area, a part of the stray light from the recording layer closer to the light incident surface of the optical disc than the recording layer on which the information reading process or the writing process is performed can be shielded, but on the side farther from the light incident surface. Stray light from the recording layer cannot be blocked. Therefore, in patent document 1, it cannot fully prevent that the offset component resulting from a stray light generate | occur | produces in a tracking error signal.

  Furthermore, when the type of optical disk (for example, BD, DVD, CD, etc.) changes, the size of stray light incident on the photodetector also changes. Therefore, in Patent Document 1, if the type of the optical disk is changed, stray light cannot be sufficiently blocked, and generation of an offset component due to stray light cannot be sufficiently prevented. Alternatively, as the stray light is shielded, the light necessary for generating the tracking error signal is also shielded, which may reduce the quality of the tracking error signal.

  The present invention has been made in view of such a situation, and provides an optical pickup and a disk device that can prevent generation of an offset component due to stray light and obtain a good tracking error signal. Objective.

  In order to achieve the above object, an optical pickup according to one aspect of the present invention includes a plurality of light sources that emit light having different wavelengths, an objective lens that collects the light on an optical disc, and information reading and writing. A diffractive portion for diffracting return light reflected from the first recording layer of the optical disc, and a light shielding portion for shielding stray light reflected from the second recording layer of the optical disc other than the first recording layer. A diffractive optical element, and a light detection unit that receives the diffracted light of the diffractive optical element and generates an output signal for generating a tracking error signal based on the diffracted light, and the light shielding units are mutually It is characterized by comprising a plurality of light shielding patterns that shield light of different wavelengths.

  According to this configuration, the light shielding portion of the diffractive optical element is configured with a plurality of light shielding patterns that shield light of different wavelengths. Therefore, the stray light is blocked by the light blocking pattern corresponding to the wavelength of the stray light and does not enter the photodetector, but the light necessary for generating the tracking error signal enters the photodetector. Accordingly, it is possible to prevent a deterioration in the quality of the tracking error signal due to the light shielding pattern. Therefore, the occurrence of an offset component due to stray light can be prevented and a good tracking error signal can be obtained.

  Further, in the above configuration, each light shielding rate of the plurality of light shielding patterns may change according to a wavelength of light incident on the diffractive optical element.

  With this configuration, for example, light incident on the diffractive optical element can be blocked by the light blocking pattern corresponding to the wavelength of stray light, but not blocked by other light blocking patterns corresponding to other wavelengths. Accordingly, it is possible to prevent light shielding necessary for generating a tracking error signal by another light shielding pattern.

  In the above configuration, the light shielding rates of the plurality of light shielding patterns may be different from each other.

  With this configuration, it is possible to suppress light shielding necessary for generating the tracking error signal by the light shielding pattern.

  In order to achieve the above object, a disc apparatus according to one aspect of the present invention includes the above-described optical pickup.

  According to this configuration, the light shielding portion of the diffractive optical element is configured with a plurality of light shielding patterns that shield light of different wavelengths. Therefore, the stray light is blocked by the light blocking pattern corresponding to the wavelength of the stray light and does not enter the photodetector, but the light necessary for generating the tracking error signal enters the photodetector. For this reason, it is possible to prevent a deterioration in the quality of the tracking error signal due to the light shielding pattern. Therefore, it is possible to prevent occurrence of an offset component due to stray light and obtain a good tracking error signal.

  According to the present invention, it is possible to provide an optical pickup and a disk device that can prevent occurrence of an offset component due to stray light and obtain a good tracking error signal.

It is a block diagram of the optical pick-up of this embodiment. It is a schematic plan view which shows arrangement | positioning of the 1st and 2nd objective lens with respect to an optical disk. It is a schematic plan view which shows the state of the return light of the laser beam for BD which injects into a hologram element. It is sectional drawing which shows an example of the return light reflected from the recording layer of 3 layer type BDXL. It is a schematic plan view which shows the state of the return light of the laser beam for DVD which injects into a hologram element. It is sectional drawing which shows an example of the return light reflected from the recording layer of 2 layer type DVD. It is a schematic plan view which shows the structural example of the hologram element of this embodiment. It is a schematic plan view which shows the other structural example of the hologram element of this embodiment. It is a schematic plan view which shows the other structural example of the hologram element of this embodiment. It is a schematic plan view which shows the structural example of the photodetector of this embodiment. 6 is a schematic plan view showing a hologram element of Comparative Example 1. FIG. 6 is a schematic plan view showing a light receiving pattern of a photodetector for a three-layer type BDXL in Comparative Example 1. FIG. 6 is a schematic plan view showing a hologram element of Comparative Example 2. FIG. 10 is a schematic plan view showing a light receiving pattern of a photodetector for a two-layer type DVD in Comparative Example 2. FIG. It is a schematic plan view which shows the light-receiving pattern of the photodetector with respect to 3 layer type BDXL in Example 1 of this embodiment. 1 is a schematic plan view showing a hologram element of Example 1. FIG. It is a schematic plan view which shows the light-receiving pattern of the photodetector with respect to 2 layer type DVD in Example 2 of this embodiment. 6 is a schematic plan view showing a hologram element of Example 2. FIG.

  Embodiments of the present invention will be described below with reference to the drawings. The optical pickup 1 of the present embodiment is a device for performing information reading processing and / or writing processing on the optical disc D. The optical pickup 1 is mounted on a disk device such as a BD recorder, a DVD recorder, a BD player, and a DVD player. Examples of types of the optical disc D that can be used for the optical pickup 1 include, for example, a single-layer type or a double-layer type BD (Blu-ray Disc) or DVD (Digital versatile Disc), BDXL (registered) having three or more recording layers Trademark), CD (Compact Disc), and the like.

  FIG. 1 is a configuration diagram of an optical pickup according to the present embodiment. As shown in FIG. 1, the optical pickup 1 of the present embodiment includes a first semiconductor laser element 11a, a second semiconductor laser element 11b, a half-wave plate 12, a beam splitter 13, and a polarization beam splitter 14. , Quarter-wave plate 15, collimating lens 16, first rising mirror 17a, second rising mirror 17b, first objective lens 18a, second objective lens 18b, front monitor photodetector 19, A hologram element 20, a cylindrical lens 21, a photodetector 22, and a signal processing unit 23 are provided.

  The first semiconductor laser element 11a is a first light source that emits a laser beam for DVD, and emits a laser beam having a wavelength of 661 nm, for example. The second semiconductor laser element 11b is a second light source that emits laser light for BD, and emits laser light having a wavelength of, for example, 405 nm.

  The half-wave plate 12 converts the S-polarized light (or P-polarized light) of the DVD laser light into P-polarized light (or S-polarized light). The beam splitter 13 reflects a part of the incident laser light and transmits the other part.

  The polarization beam splitter 14 reflects S-polarized light (or P-polarized light) of incident laser light and transmits P-polarized light (or S-polarized light). The polarization beam splitter 14 is an optical member that acts on the BD laser beam, and the DVD laser beam is transmitted regardless of its polarization state (whether S-polarized light or P-polarized light). The quarter wavelength plate 15 converts linearly polarized light (S-polarized light, P-polarized light) of laser light into circularly polarized light, and converts circularly polarized light into linearly polarized light.

  The collimating lens 16 is provided so as to be movable in the optical axis direction of the laser light (left-right direction M in FIG. 1) so that the convergence / divergence state of the laser light can be changed. The position of the collimating lens 16 is appropriately moved according to the type of the optical disc D, layer jump, and the like. Thereby, in the optical pickup 1, the influence of spherical aberration is suppressed appropriately.

  The first and second rising mirrors 17a and 17b are dichroic mirrors. The first raising mirror 17a reflects the DVD laser light that has passed through the collimating lens 16 to the first objective lens 18a. Note that the first raising mirror 17a can transmit the laser beam for BD. The second raising mirror 17b reflects the BD laser light that has passed through the collimating lens 16 and the first raising mirror 17a to the second objective lens 18b.

  The first objective lens 18a is disposed above the first rising mirror 17a, and condenses the DVD laser light incident from the first rising mirror 17a on the recording layer of the optical disc D. The second objective lens 18b is disposed above the second rising mirror 17b and condenses the BD laser light incident from the second rising mirror 17b on the recording layer of the optical disc D.

  FIG. 2 is a schematic plan view showing the arrangement of the first and second objective lenses with respect to the optical disc. As shown in FIG. 2, the first and second objective lenses 18 a and 18 b are arranged in parallel in the tangential direction of the optical disc D. The tangential direction is a substantially tangential direction of concentric or spiral tracks formed in the recording layer of the optical disc D. The first objective lens 18 a is arranged at a position where the center is placed on the reference plane A passing through the rotation center O of the optical disc D in a plan view as viewed from the normal direction of the main surface of the optical disc D. Further, the second objective lens 18b is disposed at a position shifted from the reference plane A in the tangential direction. The reference plane A is perpendicular to the main surface of the optical disc D and is parallel to the radial direction of the optical disc D. The radial direction is a direction substantially perpendicular to the tangential direction. The first and second objective lenses 18a and 18b are driven in the radial direction (lens shift) when tracking control is performed. Therefore, the lens shift direction X of the first and second objective lenses 18a and 18b is substantially parallel to the radial direction.

  The front monitor photodetector 19 is a light detection unit for detecting the laser power of the laser light emitted from the first and second semiconductor laser elements 11a and 11b, and photoelectrically converts the received laser light for DVD or BD. Generate a signal. Based on this photoelectric conversion signal, the laser power of the first and second semiconductor laser elements 11a and 11b is controlled by a controller (not shown).

  The hologram element 20 is a diffractive optical element that diffracts the light reflected by the recording layer of the optical disc D. Hereinafter, the reflected light of each laser beam reflected by the optical disc D is referred to as return light. A detailed configuration of the hologram element 20 will be described later.

  The cylindrical lens 21 is a sensor lens provided with a cylindrical surface in order to obtain a focus error signal from the return light of the laser beam for DVD or BD by the astigmatism method. The diffracted light diffracted by the hologram element 20 is incident on the photodetector 22 via the cylindrical lens 21.

  The photodetector 22 is a light detection unit that functions as a photoelectric conversion unit that receives the diffracted light of the hologram element 20 and converts the received light signal (diffracted light) into an electrical signal (photoelectric conversion signal). The photodetector 22 includes a main light receiving unit 221 and four sub light receiving units 222 (first to fourth sub light receiving units 222a to 222d) (see FIG. 8 described later). The detailed configuration of the photodetector 22 will be described later. The photoelectric conversion signal output from the photodetector 22 is sent to the signal processing unit 23.

  The signal processing unit 23 generates a reproduction signal, a focus error signal, a tracking error signal TE, and the like based on output signals of the photodetector 22 (for example, a main light receiving unit signal and a sub light receiving unit signal described later). The focus error signal and tracking error signal TE generated by the signal processing unit 23 are output to a control unit (not shown) of the optical pickup 1. A control unit (not shown) of the optical pickup 1 attaches first and second objective lenses 18a and 18b to an actuator (not shown) to perform focusing control and tracking control based on the focus error signal and the tracking error signal TE. Drive.

  In the optical pickup 1 configured as shown in FIG. 1, the laser light emitted from the first or second semiconductor laser element 11a, 11b is guided to the optical disc D, and the return light reflected by the optical disc D is guided to the photodetector 22. An optical path is formed. Below, the optical path of each laser beam is demonstrated.

  First, the optical path for BD will be described. BD laser light is emitted from the second semiconductor laser element 11 b, and S-polarized light (or P-polarized light) of the BD laser light is reflected by the polarization beam splitter 14. The reflected S-polarized light is converted into circularly polarized light by the quarter-wave plate 15. The converted circularly polarized light passes through the collimating lens 16 and the first raising mirror 17a, and is then reflected by the second raising mirror 17b. The circularly polarized light reflected by the second raising mirror 17b is condensed on the recording layer of the optical disc D (BD) by the second objective lens 18b. The condensed circularly polarized light is reflected by the recording layer and passes through the first objective lens 18a as return light Ra. Then, the return light Ra is reflected by the second raising mirror 17b, passes through the first raising mirror 17a and the collimating lens 16, and then is converted from circularly polarized light to linearly polarized light (S-polarized light, P-polarized light) by the quarter wavelength plate 15. ). The converted return light Ra passes through the polarization beam splitter 14 and the beam splitter 13, and then reaches the photodetector 22 through the sensor optical system including the hologram element 20 and the cylindrical lens 21.

  Next, the optical path for DVD will be described. The laser beam for DVD is emitted from the first semiconductor laser element 11 a, and the S-polarized light of the DVD laser light is converted into P-polarized light by the half-wave plate 12. The P-polarized light is reflected by the beam splitter 13, passes through the polarizing beam splitter 14, and then converted to circularly polarized light by the quarter wavelength plate 15. The converted circularly polarized light passes through the collimating lens 16 and is then reflected by the first rising mirror 17a. The circularly polarized light reflected by the first raising mirror 17a is condensed on the recording layer of the optical disc D (DVD) by the first objective lens 18a. The condensed circularly polarized light is reflected by the recording layer and passes through the first objective lens 18a as return light Rb. The return light Rb is reflected by the first raising mirror 17a, passes through the collimating lens 16, and then converted from circularly polarized light to linearly polarized light (S-polarized light, P-polarized light) by the quarter wavelength plate 15. The converted return light Rb passes through the polarization beam splitter 14 and the beam splitter 13, and then reaches the photodetector 22 through the sensor optical system including the hologram element 20 and the cylindrical lens 21.

  In this way, in the optical path for BD and DVD, the polarization beam splitter 14, the quarter wavelength plate 15, the collimator lens 16, and the first rising mirror 17a are provided in the forward path through which each laser beam is guided to the optical disk D. Shared. Further, in the return path where the return beams Ra and Rb of the respective laser beams reach the photodetector 22, the first raising mirror 17a, the collimating lens 16, the quarter wavelength plate 15, the polarization beam splitter 14, the beam splitter 13, the hologram element 20, The cylindrical lens 21 is shared.

  Next, the return lights Ra and Rb of each laser beam incident on the hologram element 20 will be described. In the recording layer of the optical disc D, the tracks are formed concentrically or spirally. This track acts as a diffraction grating for light incident on the optical disc D. Therefore, the return lights Ra and Rb reflected by the recording layer of the optical disc D are incident on the hologram element 20 after being split into zero-order light and ± first-order light.

  First, the return light Ra of the BD laser light will be described. FIG. 3A is a schematic plan view showing a state of return light of BD laser light incident on the hologram element. FIG. 3B is a cross-sectional view showing an example of return light reflected from a recording layer of a three-layer type BDXL. FIG. 3A is a diagram assuming that the laser beam for BD is condensed on the recording layer L1 of three layers of BDXL, as shown in FIG. 3B. As shown in FIG. 3B, in the three-layer BDXL, the recording layers provided on the substrate are referred to as L0, L1, and L2 in order from the recording layer provided on the most substrate side toward the light incident surface. In the example of FIG. 3B, since the laser beam is focused on the recording layer L1 of BDXL, the recording layer L1 is an example of the first recording layer of the present invention, and the recording layers L0 and L2 are the second recording layer of the present invention. An example. When the laser beam is focused on the recording layer L0 of BDXL, the recording layer L0 is an example of the first recording layer of the present invention, and the recording layers L1 and L2 are an example of the second recording layer of the present invention. Become. Further, when the laser beam is focused on the recording layer L2 of BDXL, the recording layer L2 is an example of the first recording layer of the present invention, and the recording layers L0 and L1 are an example of the second recording layer of the present invention. Become.

  As shown in FIG. 3A, in the return light Ra incident on the hologram element 20, a part of the zero-order light overlaps with the ± first-order light. Hereinafter, of the return light Ra, a light flux in which the ± first-order light does not overlap with the zero-order light is referred to as a first return light Ra1, and a light flux in which the zero-order light and the ± first-order light overlap is referred to as a second return light Ra2. . The first return light Ra1 and the two second return lights Ra2 are incident on the hologram element 20.

  The first return light Ra1 (the portion sandwiched between the two hatched portions in FIG. 3A) existing in the center of the return light Ra is a light beam that includes zero-order light but does not include ± first-order light, and is reflected by the optical disc D. It is an area indicating the amount of light according to the rate. In other words, this light flux does not include an AC signal (track crossing signal) component generated when light incident on the optical disc D crosses the track, and is an offset component generated due to, for example, a lens shift of the second objective lens 18b. Corresponds to luminous flux containing. On the other hand, the two second return lights Ra2 (hatched portions in FIG. 3A) present on both ends of the center of the return light Ra are light beams including the 0th order light and the ± 1st order light, and the cross-track signal component Corresponds to luminous flux containing.

  In FIG. 3A, the return light Ra (particularly the second return light Ra2) is tilted counterclockwise (counterclockwise) with respect to the direction X1 corresponding to the lens shift direction X. This is the second objective lens. This is because 18b is arranged at a position shifted in the tangential direction from the reference plane A passing through the rotation center O of the optical disc D (see FIG. 2). In FIG. 3A, the return light Ra moves in the direction X1 on the light incident surface of the hologram element 20 when the second objective lens 18b is moved (lens shift) in the tracking direction (lens shift direction X). Direction.

  The BD laser light focused on the recording layer L1 of the three BDXLs is reflected not only by the recording layer L1, but also by the recording layer L0 and the recording layer L2. These reflected lights enter the hologram element 20 as stray light. Hereinafter, the stray light that enters the hologram element 20 from the recording layer L0 provided at a position farther from the light incident surface of the BDXL (that is, the substrate side) than the recording layer L1 on which the laser light is collected is referred to as first stray light SL1. Further, the stray light incident on the hologram element 20 from the recording layer L2 provided at a position closer to the light incident surface of BDXL than the recording layer L1 (that is, the light incident surface side) is referred to as second stray light SL2.

  As shown in FIG. 3A, the first stray light SL1 is a part of the incident area of the first return light Ra1 reflected from the recording layer L1 on the light incident surface of the hologram element 20, and the light of the return light Ra. Incident into the region including the position intersecting the axis. Further, the second stray light SL2 is incident on the light incident surface of the hologram element 20 in a region including all regions where the return light Ra reflected from the recording layer L1 is incident.

  Next, the return light Rb of the laser beam for DVD will be described. FIG. 4A is a schematic plan view showing the state of the return light of the DVD laser light incident on the hologram element. FIG. 4B is a cross-sectional view showing an example of the return light reflected from the recording layer of the two-layer type DVD. FIG. 4A is a diagram assuming that the DVD laser light is focused on the recording layer L0 of the two-layer DVD as shown in FIG. 4B. In the dual-layer DVD, contrary to the case of BD, the recording layers provided on the substrate are called L0 and L1 in the order from the recording layer provided on the light incident surface side to the substrate. In the example of FIG. 4B, since the laser beam is focused on the recording layer L0 of the DVD, the recording layer L0 is an example of the first recording layer of the present invention, and the recording layer L1 is an example of the second recording layer of the present invention. It becomes. When the laser beam is focused on the recording layer L1 of the optical disc D, the recording layer L1 is an example of the first recording layer of the present invention, and the recording layer L0 is an example of the second recording layer of the present invention. .

  As shown in FIG. 4A, the return light Rb of the DVD laser light incident on the hologram element 20 has the same configuration as the return light Ra (FIG. 3A). Hereinafter, of the return light Rb, the light flux (the portion sandwiched between the two shaded portions in FIG. 4A) in which the ± first order light does not overlap with the 0th order light is referred to as first return light Rb1. Further, a light beam in which the zero-order light and the ± first-order light overlap (the hatched portion in FIG. 4A) is referred to as second return light Rb2.

  However, the return light Rb (particularly the second return light Rb2) is not inclined with respect to the direction X1. This is because the first objective lens 18a is disposed on the reference plane A passing through the rotation center O of the optical disc D (see FIG. 2). Further, in FIG. 4A, the return light Rb is moved on the light incident surface of the hologram element 20 when the first objective lens 18a is moved (lens shift) in the tracking direction (lens shift direction X). Direction.

  Also, the DVD laser light focused on the recording layer L0 of the two-layer DVD is reflected not only by the recording layer L0 but also by the recording layer L1, and enters the hologram element 20 as stray light. In the following description, the stray light incident on the hologram element 20 from the recording layer L1 provided at a position farther from the light incident surface of the DVD than the recording layer L0 on which the DVD laser light is condensed (that is, the substrate side) will be referred to as third stray light SL3. Call it. As shown in FIG. 4A, the third stray light SL3 is a part of the incident area of the first return light Rb1 reflected from the recording layer L0 on the light incident surface of the hologram element 20, and the light of the return light Rb. Incident into the region including the position intersecting the axis.

  Contrary to the case of FIG. 4B, when DVD laser light is focused on the recording layer L1 of the two-layer DVD, stray light is reflected from the recording layer L0. However, the stray light in this case is much higher than the first stray light SL1 and second stray light SL2 generated in the cases of FIGS. 3A and 3B, and the third stray light SL3 generated in the cases of FIGS. 4A and 4B. The intensity is small and the influence on the tracking error signal TE is very small. Therefore, in the present embodiment, description of stray light reflected from the recording layer L0 is omitted.

  Next, the hologram element 20 will be described in detail. FIG. 5 is a schematic plan view showing a configuration example of the hologram element of the present embodiment. As shown in FIG. 5, the hologram element 20 has a diffraction part 201 and a light shielding part 202. The diffractive portion 201 is an area where a diffraction pattern for diffracting the return lights Ra and Rb from the optical disc D and making the diffracted light incident on the light receiving surface of the photodetector 22 is formed. The diffraction unit 201 includes a first diffraction unit 201a and two second diffraction units 201b. The diffraction patterns formed in the first and second diffraction portions 201a and 201b are formed using, for example, a relief grating made up of rectangular diffraction grooves, a blazed grating made up of serrated diffraction grooves, and the like.

  The first diffractive portion 201 a guides the 0th-order diffracted light of the return light Ra and Rb to the main light receiving portion 221 of the photodetector 22 through the diffraction groove. Further, the ± first-order diffracted lights of the return lights Ra and Rb are incident on regions other than the respective light receiving surfaces of the main light receiving unit 221 and the sub light receiving unit 222 of the photodetector 22 (see FIGS. 11B and 12B described later).

  The second diffractive portion 201 b guides the 0th-order diffracted light of the return light Ra and Rb to the main light receiving portion 221 of the photodetector 22 through the diffraction groove. Further, the ± first-order diffracted light of the return light Ra of the BD laser light is guided to the first and second sub light receiving portions 222a and 222b of the photodetector 22, respectively. Further, the ± first-order diffracted light of the return light Rb of the DVD laser light is guided to the third and fourth sub light receiving portions 222c and 222d of the photodetector 22, respectively (see FIGS. 11B and 12B). The two second diffractive parts 201b are arranged in parallel with the first diffractive part 201a interposed therebetween in a direction tilted counterclockwise (counterclockwise) from the orthogonal direction Y1 of the direction X1 in FIG.

  The light shielding unit 202 is provided to shield stray light reflected from a recording layer other than the recording layer on which the laser light is collected in the optical disk D having a multilayer structure. The light shielding unit 202 is configured by combining three types of light shielding patterns 202a, 202b, and 202c that shield light of different wavelengths. The first and second light shielding patterns 202a and 202b are provided to shield stray light reflected from the multilayered BD, and the third light shielding pattern 202c is provided to shield stray light reflected from the multilayered DVD. Is provided.

  For example, in the three-layer BDXL, the first light-shielding pattern 202a is a recording layer (for example, a recording layer) provided on the side farther from the light incident surface of the BDXL than a recording layer (for example, the recording layer L1) on which information is read or written. L0) is provided to shield the first stray light SL1 reflected from (L0) (see FIG. 3B). As a result, the first stray light SL1 is prevented from entering the photodetector 22. The first light shielding pattern 202a is a substantially rectangular light shielding pattern formed in the first diffractive portion 201a. The width in the direction Y1 of the first light shielding pattern 202a is equal to or larger than the size in the direction Y1 of the first stray light SL1 on the light incident surface of the hologram element 20. The longitudinal direction of the first light shielding pattern 202a is substantially parallel to the direction X1 corresponding to the lens shift direction X of the second objective lens 18b. Therefore, even if the first stray light SL1 moves in accordance with the lens shift of the second objective lens 18b, the first stray light SL1 can be prevented from entering the photodetector 22 by the first light shielding pattern 202a.

  The width of the first light shielding pattern 202a in the direction X1 is such that one end of the second return light Ra2 (for example, the right end of the second return light Ra2 on the left side in FIG. 3A) and the other end of the second return light Ra2 (for example, FIG. 3A). To the right end of the second return light Ra2 on the right side) is set smaller than the shortest distance in the direction X1. Further, it is desirable that the width be set to a length that is less than the length that the first light-shielding pattern 202a does not overlap the second return light Ra2 even when the second objective lens 18b is lens-shifted.

  For example, in the three-layer BDXL, the second light-shielding pattern 202b is provided on the side closer to the light incident surface of the BDXL than the recording layer (for example, the recording layer L1) on which information is read or written (for example, the recording layer). L2) is provided to shield the second stray light SL2 that enters from (see FIG. 3B). Thus, the second stray light SL2 is prevented from being incident on at least the sub light receiving portion 222 (particularly, the first and second sub light receiving portions 222a and 222b) of the photodetector 22. As shown in FIG. 5, the second light-shielding pattern 202b has the return light Ra, Rb so that it does not overlap with the return light Ra, Rb in a plan view as viewed from the direction in which the return light Ra, Rb enters the hologram element 20. It is formed in the area | region of the both sides on both sides.

  The shape of the second light shielding pattern 202b is not limited to the example of FIG. 6 and 7 are schematic plan views showing other configuration examples of the hologram element of the present embodiment. The second light-shielding pattern 202b is formed in an outer region of any one of the quadrilateral shape, the circular shape, and the elliptical shape in a plan view as viewed from the direction in which the return lights Ra and Rb are incident on the hologram element 20. It may be provided. Furthermore, as shown in FIG. 6, the second light-shielding pattern 202b is a parallelogram-shaped region in which one of the two diagonal lines is parallel to the direction X1 corresponding to the lens shift direction X (for example, a square shape or a rhombus shape). It may be provided in the outer region. Alternatively, as shown in FIG. 7, the major axis may be provided in the outer region of the elliptical region that is parallel to the direction X1 corresponding to the lens shift direction X.

  The third light-shielding pattern 202c is, for example, a recording layer (for example, a recording layer) provided on a side farther from the light incident surface of the DVD than a recording layer (for example, the recording layer L0) on which information is read or written in a two-layer DVD Provided to shield the third stray light SL3 reflected from the layer L1) (see FIG. 4B). Accordingly, the third stray light SL3 is prevented from being incident on at least the sub light receiving part 222 (particularly, the third and fourth sub light receiving parts 222c and 222d) of the photodetector 22. The third light shielding pattern 202c is two substantially rectangular light shielding patterns formed in the first diffractive portion 201a. The longitudinal direction of the two third light shielding patterns 202c is substantially parallel to the direction X1 corresponding to the lens shift direction X of the first objective lens 18a. Therefore, even if the third stray light SL3 moves due to the lens shift of the first objective lens 18a, the third stray light SL3 is prevented from entering the two sub light receiving portions 222c and 222d by the third light shielding pattern 202c. Can do.

  In the present embodiment, the third light shielding pattern 202c has substantially the same shape and size as the first light shielding pattern 202a, but the scope of application of the present invention is not limited to this configuration. The width of the third light shielding pattern 202c in the direction X1 and the direction Y1 is such that at least the third light shielding pattern 202c shields the third stray light SL3 incident on the sub light receiving unit 202 (particularly, the third and fourth sub light receiving units 202c and 202d). It may be as long as possible.

  The first to third light shielding patterns 202a to 202c are formed using, for example, a metal material (Al or the like) or a dielectric material. Further, the first to third light shielding patterns 202a to 202c can be formed by, for example, a method of applying or vapor-depositing the above-described material, a method of attaching a sheet, or the like. Or you may form the part of the hologram element 20 corresponding to the 1st-3rd light shielding patterns 202a-202c using the above-mentioned material.

  Further, the light shielding rates of the first to third light shielding patterns 202a to 202c are different from each other and further exhibit wavelength dependency. The first light-shielding pattern 202a transmits, for example, light having a wavelength (for example, 661 nm) corresponding to the laser beam for DVD (light-blocking rate 0%), and converts it to light having a wavelength (for example, 405 nm) corresponding to the laser beam for BD. On the other hand, the light shielding rate is 70% or more. The second light shielding pattern 202b substantially completely shields light of each wavelength corresponding to the DVD and BD laser beams (for example, a light shielding rate of 100%). The third light shielding pattern 202c exhibits, for example, a light shielding rate of 50% or more with respect to light having a wavelength corresponding to DVD laser light, and transmits light having a wavelength corresponding to BD laser light (light shielding rate 0%). )

  As described above, the light shielding rates of the first to third light shielding patterns 202 a to 202 c change according to the wavelength of light incident on the hologram element 20. In this way, for example, light incident on the hologram element 20 can be blocked by the light blocking pattern corresponding to the wavelength of stray light, but not blocked by other light blocking patterns corresponding to other wavelengths. Therefore, it is possible to prevent light shielding necessary for generating the tracking error signal TE by another light shielding pattern.

  Further, the light shielding rates of the first to third light shielding patterns 202a to 202c are different from each other. For example, the first and third light shielding patterns 202a and 202c are formed in regions where the return lights Ra and Rb are incident. For this reason, the light blocking rates of the first and third light blocking patterns 202a and 202c are set low enough that the offset components caused by the first stray light SL1 and the third stray light SL3 do not affect the tracking error signal TE. On the other hand, the second light shielding pattern 202b is formed in a region where the return lights Ra and Rb are not incident. Therefore, the light shielding rate of the second light shielding pattern 202b is set to 100%. Accordingly, it is possible to suppress light shielding necessary for generating the tracking error signal TE by the light shielding patterns 202a, 202b, and 202c.

  Next, the photodetector 22 will be described in detail. FIG. 8 is a schematic plan view showing a configuration example of the photodetector of this embodiment. As shown in FIG. 8, the photodetector 22 includes a main light receiving part 221 and four sub light receiving parts 222 having the same shape and the same size. The four sub light receiving units 222 are arranged in a diagonal direction clockwise (clockwise) with respect to the direction X2 corresponding to the lens shift direction X with the main light receiving unit 221 interposed therebetween. The direction X2 is the direction in which the light spot formed on the light receiving surface of the photodetector 22 moves when the first or second objective lens 18a, 18b is moved (lens shift) in the tracking direction (lens shift direction). It is.

  The main light receiving unit 221 receives each 0th-order diffracted light incident from the first diffracting unit 201a and the second diffracting unit 201b, and generates a main light receiving unit signal based on the received light. The main light receiving unit 221 has four divided regions M1 to M4 obtained by dividing a substantially square light receiving region into two equal parts in the direction X2 and the orthogonal direction Y2.

  The sub light receiving unit 222 receives ± first order diffracted light incident from the second diffractive unit 201b, and generates a sub light receiving unit signal based on the received light. The sub light receiving unit signal represents an offset component resulting from the lens shift of the first or second objective lens 18a, 18b. The sub light receiving unit 222 includes a first sub light receiving unit 222a, a second sub light receiving unit 222b, a third sub light receiving unit 222c, and a fourth sub light receiving unit 222d.

  The first sub light receiving unit 222a and the second sub light receiving unit 222b receive ± first order diffracted light of the return light Ra of the BD laser light. The first sub light receiving unit 222a has two divided regions BE1 and BE2 obtained by dividing a substantially square light receiving region into two equal parts by the dividing line DL, and the second sub light receiving unit 222b has a substantially square light receiving unit. There are two divided regions BF1 and BF2 obtained by dividing the region into two equal parts by the dividing line DL. Further, the first sub light receiving unit 222a and the second sub light receiving unit 222b are arranged in a state of being inclined clockwise (clockwise) with respect to the direction X2 in FIG. This is because the second objective lens 18b is disposed at a position shifted in the tangential direction from the reference plane A perpendicular to the main surface of the optical disc D and parallel to the radial direction (see FIG. 2).

  The third sub light receiving unit 222c and the fourth sub light receiving unit 222d receive the ± first-order diffracted light of the return light Rb of the DVD laser light. The third sub light receiving part 222c has two divided areas DE1 and DE2 obtained by dividing a substantially square light receiving area into two equal parts by the dividing line DL, and the fourth sub light receiving part 222d has a substantially square light receiving part. Two divided regions DF1 and DF2 obtained by dividing the region into two equal parts by the dividing line DL are provided.

As shown in FIG. 8, the division lines DL of the sub light receiving units 222a to 222d are ± 1 next time incident from the second diffracting unit 201b when the first or second objective lens 18a, 18b is not lens-shifted. It is provided at a position that divides the folding light into two equal parts. For this reason, when the optical disc D is a BD, the tracking error signal TE in which the influence of the offset component of the lens shift of the second objective lens 18b is canceled can be obtained by the following arithmetic expression (1).
TE = MP-k * SP
= ((SM1 + SM2)-(SM3 + SM4))-k * ((SBE1-SBE2) + (SBF1-SBF2)) (1)

When the optical disk D is a DVD, the tracking error signal TE in which the influence of the offset component of the lens shift of the first objective lens 18a is canceled can be obtained by the following arithmetic expression (1).
TE = MP-k * SP
= ((SM1 + SM2)-(SM3 + SM4))-k * ((SDE1-SDE2) + (SDF1-SDF2)) (2)

  Note that k in equations (1) and (2) is a coefficient. Further, MP is a main light receiving unit signal generated by the main light receiving unit 221, and SP is a sub light receiving unit signal generated by the sub light receiving unit 222. In equations (1) and (2), each photoelectric conversion signal output from each divided region of the main light receiving unit 221 and the four sub light receiving units 222 is preceded by “S”. It is shown as

  In equations (1) and (2), the difference between the main light receiving part signal MP and the appropriately amplified sub light receiving part signal SP is obtained to obtain the offset component of the lens shift of the first objective lens 18a or the second objective lens 18b. A tracking error signal TE whose influence has been canceled is obtained.

Here, in the type in which the optical disc D has a plurality of recording layers (for example, three-layer BDXL or two-layer DVD), the recording layer that reads or writes information in the main light-receiving unit 221 and the sub-light-receiving unit 222. Stray light reflected from other than that is also incident. Therefore, an offset component due to stray light occurs in the tracking error signal TE. In particular, when this offset component occurs in the sub light receiving portion signal SP, the influence of the offset component of the lens shift cannot be accurately canceled from the tracking error signal TE. In order to prevent the influence of such stray light, in the present embodiment, the light blocking portion 202 is provided in the hologram element 20. Below, the effect of providing the light-shielding part 202 in the hologram element 20 will be described in order with reference to Comparative Example 1, Comparative Example 2, Example 1, and Example 2.
<Comparative Example 1>

  9A is a schematic plan view showing the hologram element of Comparative Example 1. FIG. FIG. 9B is a schematic plan view showing a light receiving pattern of the photodetector for the three-layer type BDXL in Comparative Example 1. The hologram element 200 of Comparative Example 1 is the same as the hologram element 20 of the present embodiment except that the light shielding portion 202 is not provided. In FIG. 9A, the return light Ra, the first stray light SL1, and the second stray light SL2 incident on the hologram element 200 are indicated by broken lines. Further, FIG. 9B is a diagram assuming a configuration (see FIG. 3B) in which the BD laser light is focused on the recording layer L1 of the three layers of BDXL.

  In Comparative Example 1, as shown in FIGS. 9A and 9B, the first stray light SL1 reflected from the recording layer L0 is diffracted by the first diffracting portion 201a, and the diffracted light is received by the main light receiving portion 221 of the photodetector 22. The light enters the surface and the region including the light receiving surface of the sub light receiving unit 222. Further, the second stray light SL2 reflected from the recording layer L3 is diffracted by the first diffracting portion 201a and the two second diffracting portions 201b. The diffracted light is incident on a region including all of the light receiving surface of the main light receiving unit 221 of the photodetector 22 and at least a part of each of the light receiving surfaces of the first and second sub light receiving units 222a and 222b. Note that the diffracted light of the first stray light SL1 and the second stray light SL2 passes through the cylindrical lens 21 and then is received by the photodetector 22, so that their incident areas are elliptical.

As described above, in the first comparative example, the sub light receiving unit 222 (particularly, the first and second sub light receiving units 222a and 222b) receives the diffracted light of the first stray light SL1 and the second stray light SL2. Therefore, in the comparative example, an offset component due to the first stray light SL1 and the second stray light SL2 is generated in the sub light receiving portion signal SP. Therefore, the influence of the offset component of the lens shift of the second objective lens 18b is determined from the tracking error signal TE. It becomes impossible to cancel accurately.
<Comparative example 2>

  10A is a schematic plan view showing the hologram element of Comparative Example 2. FIG. FIG. 10B is a schematic plan view showing a light receiving pattern of the photodetector for the dual-layer DVD in Comparative Example 2. The hologram element 200 of Comparative Example 2 is the same as the hologram element 20 of the present embodiment except that the light shielding portion 202 is not provided. In FIG. 10A, the return light Rb and the third stray light SL3 incident on the hologram element 200 are indicated by broken lines. FIG. 10B is a diagram assuming a configuration (see FIG. 4B) in which DVD laser light is focused on the recording layer L0 of the two-layer DVD.

  In Comparative Example 2, as shown in FIGS. 10A and 10B, the third stray light SL1 reflected from the recording layer L0 is diffracted by the first diffracting portion 201a, and the diffracted light is received by the main light receiving portion 221 of the photodetector 22. The light is incident on a region including all of the surfaces, all of the light receiving surfaces of the first and second sub light receiving portions 222a and 222b, and at least a part of each of the light receiving surfaces of the third and fourth sub light receiving portions 222c and 222d. . The diffracted light of the third stray light SL3 is received by the photodetector 22 after passing through the cylindrical lens 21, so that the incident area thereof is elliptical.

As described above, in Comparative Example 2, the sub light receiving unit 222 (particularly, the third and fourth sub light receiving units 222c and 222d) receives the diffracted light of the third stray light SL3. For this reason, in Comparative Example 2, since the offset component due to the third stray light SL3 is generated in the sub light receiving unit signal SP, the influence of the offset component of the lens shift of the first objective lens 18a can be accurately canceled from the tracking error signal TE. Disappear.
<Example 1>

  On the other hand, in the hologram element 20 of the present embodiment, a light shielding part 202 for shielding the first to third stray lights SL1 to SL3 is provided. Therefore, these stray lights can be prevented from entering the respective light receiving portions 221 and 222 of the photodetector 22. FIG. 11A is a schematic plan view showing the hologram element of Example 1. FIG. FIG. 11B is a schematic plan view showing a light receiving pattern of the photodetector with respect to the three-layer type BDXL in Example 1 of the present embodiment. 11A and 11B are diagrams assuming a configuration (see FIG. 3B) in which BD laser light is focused on the recording layer L1 of the three BDXL layers.

In Example 1, as shown in FIG. 11A, the first stray light SL1 reflected from the recording layer L0 is completely shielded by the first light shielding pattern 202a, and a part of the second stray light SL2 reflected from the recording layer L2 is Light is shielded by the second light shielding pattern 202b. Therefore, as shown in FIG. 11B, the first stray light SL1 does not enter the photodetector 22. The remaining part of the diffracted light of the second stray light SL2 is incident on the main light receiving unit 221 of the photodetector 22, but at least the sub light receiving unit 222 (particularly, the first and second sub light receiving units 222a and 222b). It does not enter. Therefore, it is possible to prevent the offset component due to the first stray light SL1 and the second stray light SL2 from being generated in the tracking error signal TE. Therefore, it is possible to prevent the occurrence of offset components due to the first stray light SL1 and the second stray light SL2, and to obtain a good tracking error signal TE from which the offset components due to the lens shift of the second objective lens 18b are removed. . Further, since the main light receiving unit 221 does not receive the first stray light SL1, the error of the tracking error signal TE can be further reduced.
<Example 2>

  FIG. 12A is a schematic plan view showing the hologram element of Example 2. FIG. FIG. 12B is a schematic plan view showing a light receiving pattern of the photodetector for the two-layer DVD in Example 2 of the present embodiment. FIG. 12B is a diagram assuming a configuration (see FIG. 4B) in which the laser beam for DVD is focused on the recording layer L0 of the two-layer DVD.

  In Example 2, a part of the third stray light SL3 reflected from the recording layer L1 is shielded by the third light shielding pattern 202c as shown in FIG. 12A. Therefore, as shown in FIG. 12B, the remaining part of the diffracted light of the third stray light SL3 is incident on the main light receiving part 221 of the photodetector 22, but at least the sub light receiving part 222 (particularly the third and fourth light receiving parts). The light does not enter the sub light receiving portions 222c and 222d). Therefore, it is possible to prevent the offset component due to the third stray light SL3 from being generated in the tracking error signal TE. Therefore, it is possible to prevent occurrence of an offset component due to the third stray light SL3 and obtain a good tracking error signal TE from which the offset component due to the lens shift of the first objective lens 18a is removed.

  The present invention has been described based on the embodiments. This embodiment is an exemplification, and it is understood by those skilled in the art that various modifications can be made to each component and combination of processes, and are within the scope of the present invention.

  For example, in the above-described embodiment, the configuration for preventing the influence of stray light generated in a three-layer BDXL and a dual-layer DVD has been described, but the scope of application of the present invention is not limited to this configuration. The present invention is also applicable to an optical disc having a plurality of recording layers (for example, a two-layer type BD and a DVD, a BDXL having three or more layers).

  In addition, the configuration (diffraction pattern) of each diffraction section 201 of the hologram element 20 of the above-described embodiment is merely an example, and the configuration can be changed as appropriate. For example, in the above-described embodiment, the ± first-order diffracted light of the light incident on the second diffracting portion 201b of the hologram element 20 is received by the sub light receiving portions 222 of the photodetector 22, respectively. Is not limited to this configuration. For example, one of ± 1st order diffracted lights of the return light Ra may be received by at least one of the first and second sub light receiving parts 222a and 222b of the photodetector 22. Further, one of ± 1st order diffracted lights of the return light Rb may be received by at least one of the third and fourth sub light receiving parts 222c and 222d of the photodetector 22.

  In addition, the configurations of the light receiving portions 221 and 222 of the photodetector 22 of the above-described embodiment and their light receiving surfaces are merely examples, and the configurations can be changed as appropriate. For example, in the above-described embodiment, the sub light receiving units 222 are arranged side by side in a direction oblique to the direction X2 corresponding to the lens shift direction X with the main light receiving unit 221 interposed therebetween. The scope of application of the present invention is not limited to this configuration. For example, the main light receiving unit 221 and each sub light receiving unit 222 may be arranged side by side in the direction X2.

  In the above embodiment, the first objective lens 18a and the second objective lens 18b are arranged in the tangential direction of the optical disc D (FIG. 2). However, the scope of application of the present invention is not limited to this configuration. Absent. For example, the present invention can also be applied when the first objective lens 18a and the second objective lens 18b are arranged in the radial direction. The present invention can also be applied when the number of objective lenses included in the optical pickup 1 is other than two.

  Needless to say, the type of the optical disk D that is the target of the optical pickup 1 to which the present invention is applied is not limited to that of the embodiment described above. The present invention can also be applied to the case where the optical pickup 1 is compatible with three types (or more than three types of optical discs) of optical discs D that can support CDs in addition to BDs and DVDs. It is.

  The present invention is suitable for an optical pickup compatible with a plurality of types of optical disks (for example, BD, DVD, CD, etc.).

DESCRIPTION OF SYMBOLS 1 Optical pick-up 11a 1st semiconductor laser element 11b 2nd semiconductor laser element 12 1/2 wavelength plate 13 Beam splitter 14 Polarizing beam splitter 15 1/4 wavelength plate 16 Collimate lens 17a 1st raising mirror 17b 2nd raising mirror 18a First objective lens 18b Second objective lens 19 Front monitor photodetector 20 Hologram element 201 Diffraction unit 201a First diffraction unit 201b Second diffraction unit 202 Light shielding unit 202a First light shielding pattern 202b Second light shielding pattern 202c Third light shielding pattern 21 Cylindrical lens 22 Photodetector 221 Main light receiving unit 222 Sub light receiving unit 222a First sub light receiving unit 222b Second sub light receiving unit 222c Third sub light receiving unit 222d Fourth sub light receiving unit 23 Signal processing unit Ra, Rb Return light Ra1 Rb1 first return light Ra2, Rb2 second return light SL1 first stray light SL2 second stray light SL3 third stray D optical disk L0, L1, L2 recording layer A reference plane

Claims (4)

A plurality of light sources that emit light of different wavelengths;
An objective lens for condensing the light on an optical disc;
A diffraction unit that diffracts the return light reflected from the first recording layer of the optical disc on which information is read and written, and stray light reflected from the second recording layer of the optical disc other than the first recording layer are shielded. A diffractive optical element having a light shielding portion for,
A light detection unit that receives the diffracted light of the diffractive optical element and generates an output signal for generating a tracking error signal based on the diffracted light;
With
The optical pick-up characterized in that the light-shielding part is composed of a plurality of light-shielding patterns that shield light of different wavelengths.   2. The optical pickup according to claim 1, wherein the light shielding ratios of the plurality of light shielding patterns change according to a wavelength of light incident on the diffractive optical element.   The optical pickup according to claim 1, wherein the light shielding rates of the plurality of light shielding patterns are different from each other.   A disk apparatus comprising the optical pickup according to claim 1.

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